Methods and devices for recording marks in an information layer of an optical record carrier, and record carriers for use therein

ABSTRACT

Methods and devices are described for writing to an optical record carrier, in which a mark representing recorded data is written in a phase-change layer of a record carrier by a sequence of radiation pulses. A rear heating pulse is introduced after a last write pulse and a front heating pulse is introduced before the first write pulse. The power level of the front heating pulse and the power level of the rear heating pulse may be dependent on the length of the mark to be recorded and on properties of the record carrier. The method results in a reduced jitter of the marks written, especially when writing at high recording speeds.

The invention relates to a method of recording marks representing datain a recording medium, said recording medium comprising an informationlayer having a phase which is reversibly changeable between a crystalphase and an amorphous phase, by irradiating the information layer witha pulsed radiation beam, each mark being written by a sequence of pulsescomprising at least one write pulse, the written marks being erasable byirradiating the information layer with a radiation beam having an erasepower level (e), a first write pulse of a sequence of pulses beingpreceded by a cooling pulse having a cooling power level (c) which islower than the erase power level (e), said radiation beam beinggenerated by a radiation source.

The invention also relates to a recording device for recording data inthe form of marks on a recording medium, said recording mediumcomprising an information layer having a phase which is reversiblychangeable between a crystal phase and an amorphous phase, byirradiating the information layer with a pulsed radiation beam, therecorded marks being erasable by irradiating the information layer witha radiation beam having an erase power level (e), the device comprisinga radiation source providing the radiation beam and a control unit forcontrolling the power of the radiation beam, the control unit beingoperative for providing a sequence of write pulses for writing a markand controlling the power of the radiation beam such that it has acooling power level (c) which is lower than the erase power level (e)preceding a first write pulse of a sequence of pulses.

The invention further relates to a recording medium for use in arecording device, said recording medium comprising an information layerhaving a phase which is reversibly changeable between a crystal phaseand an amorphous phase, and comprising an area containing recordingparameters.

A recording method and device as described in the preamble are knownfrom U.S. Pat. No. 5,412,626. A mark is written by a sequence of writepulses and the previously written marks between the marks being writtenare erased by applying an erase power level (e) in between thesequences. The known sequence has a cooling power level (c) immediatelybefore a first write pulse of the sequence, the cooling power level (c)being lower than the erase power level (e). The cooling power level (c)may be any power level lower than the erase power level (e), including aradiation source off level. The power level in between the write pulsesmay be any power level in the range between the erase power level (e)and the cooling power level (c). As the cooling power level (c) isimmediately before the first write pulse of the sequence, a stablerecorded mark can be formed, resulting in a mark having a low jitter.The jitter is the standard deviation of the time differences betweenlevel transitions in a digitized read signal and the correspondingtransitions in a clock signal, the time difference being normalized bythe duration of one period of said clock.

The known method is suitable for direct-overwrite on a record carrier,i.e., by writing information to be recorded in the information layer ofthe record carrier and at the same time erasing information previouslywritten in the information layer.

A method of reducing the jitter in phase-change types of record carriersis disclosed in the JPA 08287465. In this method, the edges of writepulses in sequences of pulses are shifted in time. The extent of thesetime shifts is dependent on properties of the record carrier and of therecording device. In general, the time shifts are very small as comparedwith the duration of a write pulse.

It is a drawback of the method known from U.S. Pat. No. 5,412,626 thatit does not head to sufficiently low jitter in the read signal obtainedfrom reading marks written by using the method, especially when themarks are written at high recording speeds. It is a drawback of themethod of reducing the jitter known from JPA 08287465 that it requirescomplex and expensive electronics to produce the time shifts withsufficient accuracy.

It is an object of the invention to provide a method of recording marksof the kind described in the opening paragraph, having a reduced jitterwithout the need for complex and expensive electronics.

This object is achieved when the method described in the preamble ischaracterized in that a last write pulse of a sequence is directlyfollowed by a rear heating pulse having a rear heating power level (r),the rear heating power level (r) being higher than the erase power level(e).

Instead of returning to a cooling power level (c) or an erase powerlevel (e) after a last write pulse in a sequence of pulses, a rearheating pulse having a rear heating power level (r) which is higher thanthe erase power level (e) is introduced, resulting in the jitter of themarks being smaller than the jitter of the marks recorded by means ofthe known method.

Modifying a power level in a sequence of write pulses requires lesscomplex and less expensive electronics than are required for introducingvery small shifts in time of the edges of the write pulses. Moreover,electronics for providing different power levels (such as, for example,the erase power level and the cooling power level) are already availablein recording devices, and generally only a minor modification would berequired for implementing the method according to the invention.

It may be apparent to a person skilled in the art that embodiments ofthe method according to the invention, introducing a rear heating pulsehaving more than one rear heating power level, such as, for example,step-wise descending power levels descending from the write power levelto the erase power level, also result in a reduced jitter of the marks.

The method according to the invention especially has advantages whenused in combination with a record carrier where a layer comprising anAl-alloy is replaced by a layer comprising Si and a dielectric layer,such as, for example, a layer comprising ZnS:SiO₂. These kinds of recordcarriers are known as Absorption Controlled record carriers. A typicalhigh data rate phase-change record carrier comprises a layer of anAl-alloy deposited on a substrate. Provided on top of the layercomprising an Al-alloy are, successively, at least one dielectric layer,an information layer having a phase which is reversibly changeablebetween a crystal phase and an amorphous phase (i.e., a phase-changelayer), and again at least one dielectric layer. In AbsorptionControlled record carriers, the layer comprising an Al-alloy is replacedby, successively, a layer comprising ZnS:SiO₂ and a layer comprising Sion top of the substrate. A combination of the method according to theinvention and a recording medium of the kind of Absorption Controlledrecord carriers described above results in a significant reduction ofthe jitter of the marks, especially when the marks are written at highrecording speeds.

An embodiment of the method according to the invention is characterizedin that the rear heating power level (r) of the rear heating pulse isdependent on properties of the recording medium.

The rear heating power level (r) can be assigned a fixed chosen value.Alternatively, the rear heating power level (r) can be assigned a valuewhich depends on properties of the individual record carrier on whichmarks are to be recorded. The value of the rear heating power level (r)to be used for an individual record carrier can be determined, forexample, by a test procedure where sequences of pulses, with eachsequence having a different value for the rear heating power level (r),are used to record marks, and the resulting marks are read back andanalyzed. Other test procedures can be used alternatively. Finally, theoptimal value for the rear heating power level (r) corresponding to anindividual record carrier may be recorded on that record carrier. Inthis case, the value can be directly read from the record carrier by arecording device.

A preferred embodiment of the method according to the invention forrecording marks having lengths of nT, where T represents the length ofone period of a reference clock in a data signal and n represents apredetermined natural number larger than 1, is characterized in that therear heating pulse has a first rear heating power level (r₁) when n=2, asecond rear heating power level (r₂) when n=3, and a third rear heatingpower level (r₃) when n≧4, the first rear heating power level (r₁), thesecond rear heating power level (r₂), and the third rear heating powerlevel (r₃) being dependent on properties of the recording medium.

A further reduction of the jitter is obtained when, instead of using asingle rear heating power level (r) for all marks to be recorded, therear heating power level is made dependent on the length of the marks tobe recorded. This results in a significant reduction of the jitter,especially of the shorter marks, i.e., the marks having a length of 2Tand 3T.

The rear heating power levels (r₁, r₂ and r₃) can each be assigned afixed chosen value. Alternatively, the rear heating power levels (r₁, r₂and r₃) can be assigned values which depend on properties of theindividual record carrier on which marks are to be recorded. The valuesof the rear heating power levels (r₁, r₂ and r₃) to be used for anindividual record carrier can be determined, for example, by a testprocedure where sequences of pulses, with each sequence having differentsets of values for the rear heating power levels (r₁, r₂ and r₃), areused to record marks, and the resulting marks are read back andanalyzed. Other test procedures can be used alternatively. Finally, theoptimal values for the rear heating power levels (r₁, r₂ and r₃)corresponding to an individual record carrier may be recorded on thatrecord carrier. In this case, the values can be directly read from therecord carrier by a recording device.

An embodiment of the method according to the invention is characterizedin that the first write pulse of a sequence is directly preceded by afront heating pulse having a front heating power level (f), the frontheating pulse being directly preceded by the cooling pulse having acooling power level (c), the front heating power level (f) being higherthan the erase power level (e).

A further reduction of the jitter is obtained when a front heating pulseis introduced between the cooling pulse and the first write pulse of asequence of pulses, the front heating pulse having a front heating powerlevel (f) which is higher than the erase power level (e). By introducingthis front heating pulse, a symmetry is obtained between the frontportion of a sequence of pulses and the rear portion of a sequence ofpulses. The front heating power level (f) may have a value which isequal to the rear heating power level (r), or may have a value which isdifferent from the rear heating power level (r).

An embodiment of the method according to the invention is characterizedin that the front heating power level (f) of the front heating pulse isdependent on properties of the recording medium.

The front heating power level (f) can be assigned a fixed chosen value.Alternatively, the front heating power level (f) can be assigned a valuewhich depends on properties of the individual record carrier on whichmarks are to be recorded. The value of the front heating power level (f)to be used for an individual record carrier can be determined by a testprocedure or directly read from the record carrier, as described abovein the case of the embodiment which is characterized in that the rearheating power level of the rear heating pulse is dependent on propertiesof the record carrier.

A preferred embodiment of the method according to the invention forrecording marks having lengths of nT, where T represents the length ofone period of a reference clock in a data signal and n represents apredetermined natural number larger than 1, is characterized in that thefront heating pulse has a first front heating power level (f₁) when n=2,a second front heating power level (f₂) when n=3, and a third frontheating power level (f₃) when n≧4, the first front heating power level(f₁), the second front heating power level (f₂), and the third frontheating power level (f₃) being dependent on properties of the recordingmedium.

Instead of using a single front heating power level (f) for all marks tobe recorded, the front heating power level is made dependent on thelength of the marks to be recorded. This results in a significantreduction of the jitter, especially of the shorter marks, i.e., themarks having a length of 2T and 3T.

The front heating power levels (f₁, f₂ and f₃) can each be assigned afixed chosen value. Alternatively, the front heating power levels (f₁,f₂ and f₃) can be assigned values which depend on properties of theindividual record carrier on which marks are to be recorded. The valuesof the front heating power levels (f₁, f₂ and f₃) to be used for anindividual record carrier can be determined by a test procedure ordirectly read from the record carrier, as described above in the case ofthe embodiment which is characterized in that the rear heating pulse hasa first rear heating power level (r₁) when n=2, a second rear heatingpower level (r₂) when n=3, and a third rear heating power level (r₃)when n≧4.

An embodiment of the method according to the invention is characterizedin that the cooling power level (c) of the cooling pulse is dependent onproperties of the radiation source and the recording medium.

The cooling power level (c) can be assigned a fixed chosen value.Alternatively, the cooling power level (c) can be assigned a value whichdepends on properties of the individual record carrier on which marksare to be recorded and on properties of the radiation source. The valueof the cooling power level (c) to be used for an individual recordcarrier can be determined by a test procedure as described above in thecase of the embodiment which is characterized in that the rear heatingpower level of the rear heating pulse is dependent on properties of therecord carrier.

By assigning the cooling power level (c) an optimal value which dependson properties of the individual record carrier on which marks are to berecorded and on properties of the radiation source, a fast transitionfrom the cooling power level (c) to either the front heating pulse powerlevel (f) or the power level of the first write pulse in a sequence isobtained. This results in well-defined marks, having a reduced jitter.

An embodiment of the method according to the invention for recordingmarks having lengths of nT, where T represents the length of one periodof a reference clock in a data signal and n represents a predeterminednatural number larger than 1, is characterized in that the cooling pulsehas a first cooling power level (c₁) when n=2, a second cooling powerlevel (c₂) when n=3, and a third cooling power level (c₃) when n≧4, thefirst cooling power level (c₁), the second cooling power level (c₂), andthe third cooling power level (c₃) being dependent on properties of theradiation source and the recording medium.

Instead of using a single cooling power level (c) for all marks to berecorded, the cooling power level is made dependent on the length of themarks to be recorded. This results in a significant reduction of thejitter, especially of the shorter marks, i.e., the marks having a lengthof 2T and 3T.

The cooling power levels (c₁, c₂ and c₃) can each be assigned a fixedchosen value. Alternatively, the cooling power levels (c₁, c₂ and c₃)can be assigned values which depend on properties of the individualrecord carrier on which marks are to be recorded and on properties ofthe radiation source. The values of the cooling power levels (c₁, c₂ andc₃) to be used for an individual record carrier can be determined by atest procedure as described above in the case of the embodiment which ischaracterized in that the rear heating pulse has a first rear heatingpower level (r₁) when n=2, a second rear heating power level (r₂) whenn=3, and a third rear heating power level (r₃) when n≧4.

An embodiment of the method according to the invention is characterizedin that the rear heating pulse includes a front portion having the rearheating power level (r), and a rear portion having a power level whichis lower than the erase power level (e).

It is a further object of the invention to provide a recording device ofthe kind described in the preamble, adapted for use of the methodaccording to the invention.

This object is achieved when the recording device described in thepreamble is characterized in that the control unit is operative forcontrolling the power of the radiation beam such that it has a rearheating pulse having a rear heating power level (r) directly following alast write pulse of a sequence, the rear heating power level (r) beinghigher than the erase power level (e).

An embodiment of the recording device according to the invention forrecording marks having lengths of nT, where T represents the length ofone period of a reference clock in a data signal and n represents apredetermined natural number larger than 1, is characterized in that therecording device comprises means for determining a first value for therear heating power level (r₁) when n=2, a second value for the rearheating power level (r₂) when n=3, and a third value for the rearheating power level (r₃) when n≧4, said first value for the rear heatingpower level (r₁), second value for the rear heating power level (r₂) andthird value for the rear heating power level (r₃) being dependent onproperties of the recording medium.

An embodiment of the recording device according to the invention ischaracterized in that the control unit is operative for controlling thepower of the radiation beam such that it has a front heating pulsehaving a front heating power level (f) directly preceding a first writepulse and a cooling pulse having a cooling power level (c) directlypreceding the front heating pulse, the front heating power level (f)being higher than the erase power level (e) and the cooling power level(c) being lower than the erase power level (e).

An embodiment of the recording device according to the invention forrecording marks having lengths of nT, where T represents the length ofone period of a reference clock in a data signal and n represents apredetermined natural number larger than 1, is characterized in that therecording device comprises means for determining a first value for thefront heating power level (f₁) when n=2, a second value for the frontheating power level (f₂) when n=3, and a third value for the frontheating power level (f₃) when n≧4, said first value for the frontheating power level (f₁), second value for the front heating power level(f₂) and third value for the front heating power level (f₃) beingdependent on properties of the recording medium.

It is a further object of the invention to provide a recording medium ofthe kind described in the preamble, adapted for use in the method andthe recording device according to the invention.

This object is achieved when the recording medium described in thepreamble is characterized in that the area containing recordingparameters comprises a value for the rear heating power level (r).

This object is also achieved when the recording medium described in thepreamble is characterized in that the area containing recordingparameters comprises a value for the front heating power level (f).

This object is also achieved when the recording medium described in thepreamble is characterized in that the area containing recordingparameters comprises a value for the cooling power level (c).

Using the method and the recording device according to the invention,the rear heating power level (r), the front heating power level (f) andthe cooling power level (c), respectively, can be assigned a value whichdepends on properties of the individual record carrier on which marksare to be recorded. The value for the rear heating power level (r), thefront heating power level (f) and the cooling power level (c),respectively, corresponding to the individual record carrier is recordedon the record carrier according to the invention in an area containingrecording parameters. This value can be directly read from the recordcarrier according to the invention by, for example, an embodiment of themethod and an embodiment of the recording device according to theinvention.

These and other objects, features and advantages of the invention willbe apparent from the following, more particular description ofembodiments of the invention, as illustrated in the accompanyingdrawings, where

FIGS. 1 to 4 show diagrams comprising the time-dependence of a datasignal and a corresponding control signal controlling the power levelsof the radiation beam,

FIG. 5 shows a diagram of a first recording device according to theinvention, and

FIG. 6 shows a diagram of a second recording device according to theinvention.

FIG. 1 shows diagrams comprising two signals, a digital data signal 10and a control signal 20, as used in the method according to theinvention. FIG. 1 a gives the value of the digital data signal 10 as afunction of time, the value of the signal representing information to berecorded. The vertical broken lines indicate transitions in a clocksignal of a data clock belonging to the data signal. The period of thedata clock, also called the channel bit period, is indicated by T. Whenrecording this data signal, a ‘high’ period 11 is recorded as a markhaving a length corresponding to the duration of the ‘high’ period 11,and a ‘low’ period 12 is recorded as an unwritten area, a space, betweenthe marks and having a length corresponding to the duration of the ‘low’period. In general, the length of a mark is substantially equal to thenumber of channel bit periods of the data signal times the writingspeed. The length of a mark is therefore often expressed by the numberof data clock periods when the corresponding data signal is ‘high’(e.g., 6T for a mark with a corresponding data signal being ‘high’ for 6data clock periods, and 2T for a mark with a corresponding data signalbeing ‘high’ for 2 data clock periods).

The data is written in an optical record carrier comprising aninformation layer having a phase which is reversibly changeable betweena crystal phase and an amorphous phase (i.e., a phase-change layer). Themarks representing the data are written along a track in the informationlayer by irradiating the information layer with a pulsed radiation beam.The marks are areas of the information layer having opticalcharacteristics which are different from their surroundings, which makesoptical reading of these marks possible.

FIG. 1 b shows a control signal 20 corresponding to the data signal 10in a first embodiment of the invention. The control signal 20 is usedfor modulating the power of a radiation beam with which the marks arebeing written in the information layer, where it is assumed that thepower level of the radiation beam is proportional to the level of thecontrol signal.

FIG. 1 b shows two sequences of pulses for successively writing a 6Tmark and a 2T mark. Each sequence of pulses starts with a cooling pulse27 having a cooling power level (c) 17. The power level in between thesequences is at an erase power level (e) 16. The power level in betweenthe write pulses 21, 22 and 23, with the write pulses having a writepower level 14, is at the cooling power level (c) 17. The last writepulse of a sequence 23 is directly followed by a rear heating pulse 24having a rear heating power level (r) 15, and the first write pulse of asequence 22 is directly preceded by a front heating pulse 25 having afront heating power level (f) 13. When recording a 2T mark, only asingle write pulse 26 is applied, said single write pulse 26 being thefirst write pulse in the sequence and the last write pulse in thesequence at the same time.

In a preferred embodiment of the invention, the rear heating power level(r) and the front heating power level (f) are made dependent on thelength of the marks to be recorded. FIG. 2 shows a first control signal31 corresponding to a first data signal 30 and a second control signal33 corresponding to a second data signal 32 in this preferred embodimentof the invention.

FIG. 2 a shows a data signal 30 comprising successively a 2T mark and a3T mark to be recorded. FIG. 2 b shows the corresponding control signal31. The front heating pulse 252 of the sequence of pulses for recordinga 2T mark has a first front heating power level (f₁) 342, while thefront heating pulse 253 of the sequence of pulses for recording a 3Tmark has a second front heating power level (f₂) 341. FIG. 2 c shows adata signal 32 comprising again the 2T mark now followed by a 4T mark tobe recorded. FIG. 2 d shows the corresponding control signal 33. Therear heating pulse 242 of the sequence of pulses for recording a 2T markhas a first rear heating power level (r₁) 351, while the rear heatingpulse 244 of the sequence of pulses for recording a 4T mark has a secondrear heating power level (r₃) 352.

In this example, the rear heating pulse 242 of the sequence of pulsesfor recording a 2T mark has a rear heating power level which is equal tothat of the rear heating pulse 243 of the sequence of pulses forrecording a 3T mark. However, the rear heating pulse 242 of the sequenceof pulses for recording a 2T mark may alternatively have a rear heatingpower level which is different from that of the rear heating pulse 243of the sequence of pulses for recording a 3T mark. Likewise, the frontheating power level of the front heating pulse 253 for recording a 3Tmark may alternatively have a value which is different from that of thefront heating power level of the front heating pulse 254 for recording a4T mark, although they have an equal value in this example.

In the example shown in FIG. 2, marks having a length longer than 4Twill be recorded, using a front heating pulse having a front heatingpower level which is equal to that used for recording a 4T mark andusing a rear heating pulse having a rear heating power level which isequal to that used for recording a 4T mark. It may be apparent to aperson skilled in the art that marks having a length longer than 4T mayalternatively be recorded, using front heating power levels and rearheating power levels which are optimized for each individual marklength. Besides the rear heating power level (r) and the front heatingpower level (f), also the cooling power level (c) of the cooling pulsemay be dependent on the length of the marks to be recorded.

FIG. 3 a shows a data signal 40 comprising successively a 2T mark and a3T mark to be recorded. FIG. 3 b shows the corresponding control signal41. The cooling pulse 271 of the sequence of pulses for recording a 2Tmark has a first cooling power level (c₁) 44, while the cooling pulse272 of the sequence of pulses for recording a 3T mark has a secondcooling power level (c₂) 45.

FIG. 4 shows an embodiment of the invention where the rear heating pulseincludes a front portion and a rear portion. FIG. 4 a shows a datasignal 50 comprising a 3T mark to be recorded. FIG. 4 b shows thecorresponding control signal 51. The last write pulse of a sequence 23is directly followed by a front portion 54 of the rear heating pulse,having a rear heating power level (r) 15, and subsequently by a rearportion 55 of the rear heating pulse. The rear portion 55 of the rearheating pulse has a power level 53 which is lower than the erase powerlevel (e) 16.

FIG. 5 shows a recording device according to the invention for recordingdata on a disc-shaped optical record carrier 150. Alternatively, therecord carrier may be in the form of a tape. A data signal S_(D),comprising the information to be recorded in the form of marks, isconnected to a control unit 60. A current source 61 within the controlunit 60 has five outputs, A, B, C, D and E. Output A provides a currentwhich, when fed to a radiation source 151, through a control signalS_(C), will result in a radiation beam 152 having an erase power level(3). Likewise, outputs B, C, D and E provide currents resulting in thewrite power level, the rear heating power level (r), the front heatingpower level (f) and the cooling power level (c), respectively. Thecurrent of each output A, B, C, D, and E can be selected by a switchunit62. The switchunit 62 is operated by a pattern generator 63 controlledby the data signal S_(D) and a clock signal S_(K). The pattern generator63 transforms the data signal S_(D) into sequences of pulses having acooling power level (c), a write power level, a front heating powerlevel (f), a rear heating power level (r), and an erase power level (e)in accordance with a desired pattern. The clock signal S_(K) is obtainedfrom a clock generator 158. When the recording device is used forwriting at a single speed, the clock generator 158 is preset at a fixedfrequency. When writing at a variable speed, the frequency of the clockgenerator 158 will vary with the actual writing speed.

The control signal S_(C), provided at the output of the control unit 60and carrying the sequences of write pulses, is connected to theradiation source 151. The control signal S_(C) controls the power of theradiation beam 152 generated by the radiation source 151. The radiationbeam 152 is focused by a lens 153 onto an information layer 501 of therecord carrier 150. The disc-shaped record carrier 150 is rotated aroundits center by a motor 154.

This embodiment of a recording device according to the invention issuitable for executing the embodiments of the method according to theinvention as shown in FIG. 1, using a single front heating power level(f) and a single rear heating power level (r) which are independent ofthe length of the marks to be recorded.

FIG. 6 shows a recording device according to the invention for recordingon a disc-shaped optical record carrier 150, using values for the frontheating power level (f) and the rear heating power level (r) which aredependent on the length of the marks to be recorded. The data signalS_(D) is connected to a unit 70 comprising determination means. Thisunit 70 analyzes the data signal S_(D) and determines the length of themarks to be recorded. Dependent on the length of a mark to be recorded,appropriate current settings for the outputs C (rear heating powerlevel) and D (front heating power level) of the current source 61 areselected and transferred to the current source 61 through signal 71. Inthis way, instead of a single current, resulting in a single power levelof the radiation beam, both output C and output B may supply differentcurrents, resulting in different power levels of the radiation beam, thevalue of the currents being dependent on the length of the marks to berecorded.

Besides being dependent on the length of the marks to be recorded, thefront heating power level (f) and the rear heating power level (r) mayalso be dependent on properties of the recording medium. Informationconcerning the optimal settings of the power levels for a specificrecord carrier on which data is to be recorded may be supplied to unit70 through signal 72. The information concerning the optimal settings ofthe power levels may be supplied, for example, by a test proceduredetermining the optimal settings or, alternatively, may be read directlyfrom an area containing recording parameters on the record carrier.

1. A method of recording marks representing data in a recording medium,said recording medium comprising an information layer having a phasewhich is reversibly changeable between a crystal phase and an amorphousphase, by irradiating the information layer with a pulsed radiationbeam, each mark being written by a sequence of pulses comprising atleast one write pulse, the written marks being erasable by irradiatingthe information layer with a radiation beam having an erase power level,a first write pulse of a sequence of pulses being preceded by a coolingpulse having a cooling power level which is lower than the erase powerlevel, said radiation beam being generated by a radiation source,characterized in that a last write pulse of a sequence is directlyfollowed by a rear heating pulse having a rear heating power level, therear heating power level being higher than the erase power level, andthe rear heating power level being a different level from said lastwrite pulse.
 2. A method an claimed in claim 1, characterized in thatthe rear heating power level of the rear heating pulse is dependent onproperties of the recording medium.
 3. A method as claimed in claim 1for recording marks having lengths of nT, where T represents the lengthof one period of a reference clock in a data signal and n represents apredetermined natural number larger than 1, each mark being written by asequence of (n−1) write pulses, characterized in that the rear heatingpulse has a first rear heating power level when n=2, a second rearheating power level when n=3, and a third rear heating power level whenn≧4, the first rear heating power level, the second rear heating powerlevel, and the third rear heating power level being dependent onproperties of the recording medium.
 4. A method as claimed in claim 1,characterized in that the first write pulse of a sequence is directlypreceded by a front heating pulse having a front heating power level,the front heating pulse being directly preceded by the cooling pulsehaving a cooling power level, the front heating power level being higherthan the erase power level.
 5. A method as claimed in claim 4,characterized in that the front heating power level of the front heatingpulse is dependent on properties of the recording medium.
 6. A method asclaimed in claim 4 for recording marks having lengths of nT, where Trepresents the length of one period of a reference clock in a datasignal and n represents a predetermined natural number larger than 1,each mark being written by a sequence of (n−1) write pulses,characterized in that the front heating pulse has a first front heatingpower level when n=2, a second front heating power level when n=3, and athird front heating power level when n≧4, the first front heating powerlevel, the second front heating power level, and the third front heatingpower level being dependent on properties of the recording medium.
 7. Amethod as claimed in claim 4 for recording marks having lengths of nT,where T represents the length of one period of a reference clock in adata signal and n represents a predetermined natural number larger than1, each mark being written by a sequence of (n−1) write pulses,characterized in that the cooling pulse has a first cooling power levelwhen n=2, a second cooling power level when n=3, and a third coolingpower level when n≧4, the first cooling power level, the second coolingpower level, and the third cooling power level being dependent onproperties of the radiation source and the recording medium.
 8. A methodas claimed in claim 1, characterized in that the cooling power level ofthe cooling pulse is dependent on properties of the radiation source andthe recording medium.
 9. A method as claimed in claim 1, characterizedin that the rear heating pulse includes a front portion having the rearheating power level, and a rear portion having a power level which islower than the erase power level.
 10. A method of recording marksrepresenting data in a recording medium, said recording mediumcomprising an information layer having a phase which is reversiblychangeable between a c crystal phase and an amorphous phase, byirradiating the information layer with a pulsed radiation beam, eachmark having a length of nT, where T represents the length of one periodof a reference clock in a data signal and n represents a predeterminednatural number larger than 1, the marks being written by a sequence ofpulses comprising (n−1) write pulses, the written marks being erasableby irradiating the information layer with a radiation beam having anerase power level, a first write pulse of a sequence of pulses beingpreceded by a cooling pulse having a cooling power level which is lowerthan the erase power level, said radiation beam being generated by aradiation source, characterized in that the cooling pulse has a firstcooling power level when n=2, a second cooling power level when n=3, anda third cooling power level when n≧4, wherein the first second and thirdcooling power levels are not all the same level and the first coolingpower level, the second cooling power level, and the third cooling powerlevel being dependent on properties the radiation source and of therecording medium.
 11. A method as claimed in claim 10, characterized inthat the first cooling power level is substantially equal to either thesecond cooling power level or the third cooling power level.
 12. Arecording device for recording data in the form of marks on a recordingmedium, said recording medium comprising an information layer having aphase which is reversibly changeable between a crystal phase and anamorphous phase, by irradiating the information layer with a pulsedradiation beam, the recorded marks being erasable by means ofirradiating the information layer with a radiation beam having an erasepower level, the device comprising a radiation source providing theradiation beam and a control unit for controlling the power of theradiation beam, the control unit being operative for providing asequence of write pulses for writing a mark and controlling the power ofthe radiation beam such that it has a cooling power level which is lowerthan the erase power level preceding a first write pulse of a sequenceof pulses, characterized in that the control unit is operative forcontrolling the power of the radiation beam such that it has a rearheating pulse having a rear heating power level directly following alast write pulse of a sequence, the rear heating power level beinghigher than the erase power level and the rear heating power level beinga different level from said last write pulse.
 13. A recording device asclaimed in claim 12, characterized in that the recording devicecomprises means for determining a value for the rear heating powerlevel, which value for the rear heating power level depends onproperties of the recording medium.
 14. A recording device as claimed inclaim 13, said recording medium comprising said information layer havingsaid phase which is reversibly changeable between said crystal phase andsaid amorphous phase, and said recording medium further comprising anarea containing recording parameters, characterized in that the areacontaining recording parameters comprises a value for the rear heatingpower level.
 15. A recording device as claimed in claim 12 for recordingmarks having lengths of nT, where T represents the length of one periodof a reference clock in a data signal and n represents a predeterminednatural number larger than 1, characterized in that the recording devicecomprises means for determining a first value for the rear heating powerlevel when n=2, a second value for the rear heating power level whenn=3, and a third value for the rear heating power level when n≧4, saidfirst value for the rear heating power level, second value for the rearheating power level and third value for the rear heating power levelbeing dependent on properties of the recording medium.
 16. A recordingdevice as claimed in claim 12, characterized in that the control unit isoperative for controlling the power of the radiation beam such that ithas a front heating pulse having a front heating power level directlypreceding a first write pulse and a cooling pulse having a cooling powerlevel directly preceding the front heating pulse, the front heatingpower level being higher than the erase power level and the coolingpower level being lower than the erase power level.
 17. A recordingdevice as claimed in claim 16, characterized in that the recordingdevice comprises means for determining a value for the front heatingpower level, which value for the front heating power level depends onproperties of the recording medium.
 18. A recording device as claimed inclaim 17, said recording medium comprising said information layer havingsaid phase which is reversibly changeable between said crystal phase andsaid amorphous phase, and said recording medium further comprising anarea containing recording parameters, characterized in that the areacontaining recording parameters comprises a value for the front heatingpower level.
 19. A recording device as claimed in claim 16 for recordingmarks having lengths of nT, where T represents the length of one periodof a reference clock in a data signal and n represents a predeterminednatural number larger than 1, characterized in that the recording devicecomprises means for determining a first value for the front heatingpower level when n=2, a second value for the front heating power levelwhen n=3, and a third value for the front heating power level when n≧4,said first value for the front heating power level, second value for thefront heating power level and third value for the front heating powerlevel being dependent on properties of the recording medium.
 20. Arecording device as claimed in claim 16, characterized in that therecording device comprises means for determining a value for the coolingpower level, which value for the cooling power level depends onproperties of the recording medium.
 21. A recording device as claimed inclaim 20, said recording medium comprising said information layer havingsaid phase which is reversibly changeable between said crystal phase andsaid amorphous phase, and said recording medium further comprising anarea containing recording parameters, characterized in that the areacontaining recording parameters comprises a value for the cooling powerlevel.
 22. A recording device as claimed in claim 16 for recording markshaving lengths of nT, where T represents the length of one period of areference clock in a data signal and n represents a predeterminednatural number larger than 1, characterized in that the recording devicecomprises means for determining a first value for the cooling powerlevel when n=2, a second value for the cooling power level when n=3, anda third value for the cooling power level when n≧4, said which firstvalue for the Cooling power level, second value for the cooling powerlevel and third value for the cooling power level being dependent onproperties of the radiation source and the recording medium.
 23. Arecording device as claimed in claim 12, characterized in that thecontrol unit is operative for providing the rear heating pulse andcontrolling the power of the radiation beam such that the rear heatingpulse includes a front portion having the rear heating power level, anda rear portion having a power level which is lower than the erase powerlevel.
 24. A recording device for recording data in the form of marks ona recording medium, said recording medium comprising an informationlayer having a phase which is reversibly changeable between a crystalphase and an amorphous phase, and said marks having lengths of nT, whereT represents the length of one period of a reference clock in a datasignal and n represents a predetermined natural number larger than 1, byirradiating the information layer by a pulsed radiation beam, therecorded marks being erasable by irradiating the information layer witha radiation beam having an erase power level, the device comprising aradiation source providing the radiation beam and a control unit forcontrolling the power of the radiation beam, the control unit beingoperative for providing a sequence of write pulses for writing a markand controlling the power of the radiation beam such that it has coolingpower level which is lower than the erase power level preceding a firstwrite pulse of a sequence of pulses, characterized in that the recordingdevice comprises means for determining a first value for the coolingpower level when n=2, a second value for the cooling power level whenn=3, and a third value for the cooling power level when n≧4, said firstvalue for the cooling power level, second value for the cooling powerlevel and third value for the cooling power level being dependent onproperties of the radiation source and the recording medium, wherein thefirst, second and third cooling power levels are not all the same level.25. A recording device as claimed in claim 24, characterized in that thefirst value for the cooling power level is substantially equal to eitherthe second value for the cooling power level or the third value for thecooling power level.